Conventionally, there have been known electric power steering apparatuses including a water detection element provided in a gear housing to detect water leaked into the gear housing. An output signal of the water detection element is transmitted to a determination circuit provided outside the gear housing via wirings laid inside and outside the gear housing. The determination circuit determines whether there is the leak of the water into the gear housing based on the output signal of the water detection element. PTL 1 discusses one example regarding the above-described technique.